The objective of the proposed research is to define and elucidate the mechanism of action of the various proteins, both cellular and viral, involved in adenovirus DNA replication. Several approaches are being taken. We are attempting to characterize in detail the structure of the 55K protein (terminal protein) covalently attached to the ends of adenovirus DNA. This protein appears to first be synthesized as an 87K precursor. The structural relationship between the 87K and 55K proteins as well as site of DNA linkage within the protein are being examined. In another study we have shown that the 87K protein is viral coded, mapping in a newly discovered early region between 16-22 map units on the 1 strand. The region is the physical site of several DNA negative mutants (N complementation group) and the relationship between these mutants and the terminal protein, if any, is being explored. In vivo experiments designed to elucidate the N group phenotype in more detail and in vitro experiments analyzing the terminal proteins from mutant viruses are underway. We are also examining DNA synthesis in an in vitro system derived from the ts mutants and non-complementing serotypes (Ad 5 and Ad 12) in an effort to begin to define some of the factors required for replication.